1. Field of the Invention
The invention relates to Pt/zeolite catalyst materials.
2. Description of Related Art
Developing alternative fuels for motor vehicles has become an increasingly important goal for the automotive industry. In one type of fuel cell, methanol is used as a stored fuel and the combustion fuel, hydrogen, is obtained from methanol. A methanol reforming reactor, known in the art, produces hydrogen from methanol. However, for fuel cell applications, the outlet gas mixture from a methanol reforming reactor usually has an undesireably high carbon monoxide (CO) content.
One possible solution to this problem involves catalytically removing CO by selective oxidation. Reactors and processes suitable for this purpose are disclosed, for example, in published German applications DE 43 34 981 and DE 43 34 983. The Pt/Al.sub.2 O.sub.3 catalysts disclosed therein are useful for the selective oxidation of CO. However, in certain applications, such as at the optimum operating temperature of about 110.degree. C., these catalysts are subject to slow poisoning from CO occupying the catalytically active center. This leads to an intolerable rise in the CO starting concentration, even after relatively short operating times.
In the above-mentioned German applications, the use of a Pt/zeolite catalyst material has been proposed. However, the Pt/zeolite catalyst materials obtainable to date have not yet shown a satisfactory effect in reducing CO levels. Accordingly, there is a need in the art for methods and compounds to reduce the CO content from methanol reforming reactors that produce hydrogen, especially in fuel cell applications.
Platinum/zeolite catalysts have already been used in the automobile industry, however, that use has been in the treatment of exhaust. For example, an abstract of Japanese application JP 5317722 A discusses the use of Pt/zeolite catalyst material for removing nitrogen oxides from the exhaust gas of combustion engines. Also, published German application DE 37 16 446 A1 discusses a process for preparing a Pt/zeolite catalyst material intended for use in a diesel soot filter. The filter has a catalytically active coating for the purpose of reducing the ignition temperature.
Platinum/zeolite catalysts have also been used in methods for preparing certain chemical compounds. For example, processes for preparing Pt/zeolite catalyst materials for the hydroisomerization of hydrocarbons or for the dehydrogenation of alkanes are described in German applications DE 1 273 511 and DE 2 230 615. Also, in a method for preparing a diester of carbonic acid, published European application EP 0 501 507 A2 discusses the use of zeolite catalyst materials containing ions of a metal of the platinum group. In the use of these catalysts, carbon monoxide is brought into contact with a nitrite in gas phase in the presence of the catalyst. The European application notes a number of possible ways of preparing the Pt/zeolite catalyst materials.
Thus, while Pt/zeolite catalyst materials have been used in certain applications, their successful use to reduce CO levels for fuel cells providing hydrogen from methanol has not been disclosed.